What is the sum of the first 28 terms in the following sequence? 1, 1, 2, 1, 3, 2, 1, 4, 3, 2, 1, 5, 4, 3, 2…
What is the sum of the first 28 terms in the following sequence?
1, 1, 2, 1, 3, 2, 1, 4, 3, 2, 1, 5, 4, 3, 2, ......
83
84
85
86
Solution
The series is built in descending blocks: 1 | 1,2 | 1,3,2 | 1,4,3,2 | 1,5,4,3,2 | 1,6,5,4,3,2 | 1,7,6,5,4,3,2. The block sizes 1+2+3+4+5+6+7 = 28 terms. Their total sum = 84.